1. Technical Field
This invention relates generally to biasing circuits and, in particular, to constant current biasing circuits.
2. Related Art
A resistor and a diode are commonly used with a bias voltage to create a biasing current for use in numerous types of circuits including amplifiers. As the bias voltage is applied to the resistor diode biasing circuit, a biasing current results. A disadvantage of using a diode in the biasing circuit is that the diode does not create a linear relationship between the bias voltage and the biasing current. Additionally, the dynamic range of the biasing current is limited by a resistor diode biasing circuit.
The diode in the resistor diode biasing circuit also results in biasing current fluctuations when the temperature changes. The biasing current fluctuations have an adverse effect on the circuit being biased and must be tolerated or have additional temperature compensation circuitry added. Thus, there is a need in the art for a biasing circuit that has a linear relationship between the biasing voltage and biasing current and that functions over a broad dynamic range and is unaffected by temperature changes.